Implantable medical devices (IMDs) have become increasingly sophisticated and more capable over time. The initial implantable cardiac devices were typically pacemakers and/or implantable cardioverter-defibrillators (ICDs), which provided electrical pacing pulses to the heart at a generally fixed rate. As the technology has developed, more advanced pacing systems have been planted into patients. These more advanced systems are capable of providing pacing pulses to the heart only when the pacing system determines that the heart will not provide an intrinsic heart beat. Moreover, such advanced pacemakers are also able to adjust the pacing rate to accommodate different levels of physical activity and corresponding metabolic demand of the patient.
Typically, IMDs are equipped with sensors, which provide signals that are used by the IMD to determine the pacing rate. Such sensors include activity sensors, including accelerometers, metabolic rate sensors, including minute ventilation sensors, electrical sensors, including impedance sensors, pressure sensors, and the like. IMDs may also use the sensors to perform automatic testing functions by measuring various conditions of the heart.
When operating properly, an IMD will provide beneficial treatment to a patient. However, technical anomalies with the IMD device or any of its leads may cause the IMD to either fail to deliver appropriate treatment or deliver unnecessary treatment. Failure of pace/sense and high-voltage leads are a leading cause for the delivery of inappropriate therapies to patients that have IMDs. This problem has been identified by numerous physicians to be of paramount importance to the safety of the use of IMDs.
While daily high-voltage lead checks are able to determine high-voltage conductor failures, there are currently no existing methods to accurately detect intermittent low-voltage conductor failures. It is difficult to identify intermittent low-voltage conductor failures with a typical daily check because daily lead impedance checks are usually derived from the average value of the impedance data and do not consider the distribution of the impedance samples. Moreover, the daily check may not be taking measurements at times when the failures occur. For example, if the particular failure only occurs during a particular point during the cardiac cycle or between cardiac cycles, the daily check may not be testing at the exact time during which the failure occurs. Additionally, failures may occur at a certain time of day, for example, at night when the patient is lying down, or when the patient is making some specific type of physical movement. These various times or physical positions may trigger failures referred to as intermittent make/break connections. Intermittent make/break connections occur when shorts or open circuits occur within one or more of the leads due to a bad contact or when there is a make/break connection or contact between an intact lead and the cardiac tissue itself. This condition often leads to the production of sensing artifacts and the false detection of fast rhythms. Thus, it is unlikely that intermittent lead failures triggered by such transient conditions will be identified through periodic daily lead checks. Furthermore, because a tested vector is generally bipolar, it would not be possible to identify whether the tip conductor or the ring conductor has failed.